This invention relates to a time delay assembly for blasting signal transmission tube.
In detonating a plurality of blasting charges it is often required that the timing of such detonations be controlled precisely. This is true, for example, in blasting quarries where sequential delays between charges must be controlled within milliseconds. In order to control such timing of charges, transmission lines are deployed from a central initiating point to send a signal to detonate the individual blasting charges. Normally, these lines consist of one or more main trunk lines connected to a plurality of down lines.
Timing of the detonating signal is normally accomplished by using preselected lengths of known signal velocity transmission lines, and by utilizing signal delay units where necessary.
The manner of connection of the signal transmission lines, for example, between a trunk of lines and a plurality of down lines, depends on the type of transmission line utilized. Conventional destructing combustible fuses and detonation cords may be connected by tying together the line ends. In some cases supplementary charges are utilized to assure that the signal is transmitted. A supplementary charge device is as disclosed in U.S. Pat. No. 4,481,884. Where additional delay time is required, a delay unit may be utilized, for example, as disclosed in U.S. Pat. No. 2,736,263.
Non-destructing transmission tubes may also be utilized to carry a detonating signal, for example, as disclosed in U.S. Pat. No. 3,590,739. The detonating signal transmission tube disclosed therein is sold under the trademark "Nonel" and is sometimes referred to as "shock tube". As used herein, there term "signal transmission tube" refers to any detonating or deflagrating signal transmission line comprising a flexible hollow tube which can carry a detonating or deflagrating signal along its interior, which signal does not destroy the tube. Such signal transmission tube may be any of the different available tubes, for example, shock tube having a detonating powder coated on the inner periphery of the tube, as disclosed in the aforementioned U.S. Pat. No. 3,590,739, transmission tube containing a combustible gas within the hollow tube, transmission tube containing a combustible substance carried on a line inside the tube, or a transmission tube having a deflagrating substance coated on the inside of the tube as disclosed in co-pending U.S. patent application Ser. No. 811,731 assigned to the assignee of the present application.
The term "signal" when used in connection with the aforementioned transmission tube is intended to refer to both the detonating shock wave or deflagrating flame front which is transmitted along the interior of the shock tube by combustion of the reactive substances contained therein.
Conventional delay elements have not been suitable for use with shock tube because of the low intensity of the incoming transmission tube signal and problems in creating an outgoing transmission tube signal.
The low transmission tube signal intensity also causes problems in connecting the tubes. Unless the transmission tube signal is carefully directed and controlled, it may dissipate as it passes from one tube to another and fail to initiate a signal in the second tube. In addition, the presence of contaminating elements such as water may cause the signal to dissipate. As a result, field connections of signal transmission tubes have heretofore been unsatisfactory.
It is therefore an object of the present invention to provide an improved signal delay unit for signal transmission tube.
It is another object of the present invention to provide a delay unit for signal transmission tube which has improved reliability.
It is a further object of the present invention to provide a delay unit for signal transmission tube which may be utilized in field installations under adverse environmental conditions.
Other objects will be in part obvious and in part pointed out in more detail hereinafter.
A better understanding of the objects, advantages, features, properties and relations of the invention will be obtained from the following description and accompanying drawings which set forth certain illustrative embodiments and are indicative of the various ways in which the principles of the invention are employed.